1. Field of the Invention
This invention relates to a tank joint part and a process for manufacturing an annular molded product of resins. More particularly, it relates to any of tank joint parts attached to a fuel tank for connecting a fuel hose or the like to the fuel tank. The tank joint part may be in the form of, for example, a pipe or valve. This invention relates also to a process for manufacturing an annular molded product of a resin containing nano-layered mineral oriented substantially at right angles to its radius.
2. Description of the Related Art
The integration of automotive parts has been promoted. For example, there has been an increase of cases in which devices made of a resin, such as filler valves and onboard refueling vapor recovery (ORVR) valves, are attached to an automobile fuel tank made of a resin for joining fuel hoses to it. An automobile fuel tank often has a multilayer wall including a layer formed of a material of low fuel permeability, such as an ethylene-vinyl alcohol copolymer (EVOH), to cope with the recent gasoline evaporative emission regulations. It often has an outer surface layer formed of high-density polyethylene (HDPE) for water resistance and economical reasons.
A fuel filler valve is usually made of polyamide 12 reinforced with glass fiber (PA12GF) because of its low fuel permeability. Such a valve is, however, very low in weldability to the outer surface layer of HDPE of the fuel tank. A welding member is, therefore, interposed between the outer surface layer of the tank and the filler valve. The welding member is usually of modified polyethylene which is easily weldable to both of HDPE and PA12 GF. Such related art is disclosed in Japanese Patent No. 2,715,870. German Patent DE 195 35 413 C1 discloses a multilayer welding member of HDPE, or modified HDPE.
A polyethylene resin, such as modified polyethylene, HDPE or modified HDPE, is, however, of high fuel permeability. A welding member of such a resin material gives a tank joint part of higher fuel permeability which may cancel the advantage of a fuel tank having a wall layer of a material of low fuel permeability as stated above, and make it fail to satisfy the evaporative emission regulations which are particularly strict in the United States.
It is an object of this invention to overcome the drawbacks of the related art as stated above.
Modified polyethylene is easily weldable to both the outer surface of a fuel tank and the main body of a tank joint part, as stated. Moreover, the inventors of this invention have found that modified polyethylene is a material in which layers of a nano-layered mineral are easily dispersible, particularly when polymer intercalation is employed, among resins expected to exhibit good weldability or joinability.
It is generally said that a nano-composite prepared from a resin and a nano-layered mineral gives a molten resin which is low in fluidity (and in moldability) if its mineral content is high. Modified polyethylene is, however, a material in which such a mineral can be easily dispersed. Moreover, it has been found that the specifically controlled orientation of such a mineral in the modified polyethylene lowers its fuel permeability dramatically, even if the proportion of the mineral may be so small as not to affect the fluidity or moldability of the molten resin.
According to a first aspect of this invention, there is provided a tank joint part for connecting a device to a fuel tank having an outer surface formed of a resin, the joint part comprising a welding member formed from a resin and welded to the outer surface of the tank and a main body formed of a resin and welded or otherwise joined to the welding member, the resin of the welding member being modified polyethylene in which a nano-layered mineral is dispersed in layers.
The welding member of modified polyethylene is easily weldable to the outer surface of a fuel tank formed of, for example, HDPE and is also easily weldable or otherwise joinable to the main body of the tank joint part formed from, for example, glass fiber-reinforced polyamide 12. Because the nano-layered mineral can be satisfactorily dispersed in modified polyethylene, the fuel impermeability of the welding member is greatly improved due to barrier of nano-layered mineral against fuel. The proportion of the mineral can be small enough to ensure the fluidity (and moldability) of the molten modified polyethylene used to mold the tank joint part. Moreover, the welding member hardly swells in volume with fuel, so that hardly any cracking or fracture occurs between the welding member and the main body of the joint part, or between the welding member and the outer surface of the fuel tank. Incidentally, HDPE can be added to the modified polyethylene containing a nano-layered mineral dispersed therein to the extent not affecting the action of the mineral.
According to a second aspect of this invention, the nano-layered mineral are oriented substantially at right angles to the direction of any possible permeation of fuel from the welding member. Such orientation enables the mineral to produce the best result in preventing the permeation of fuel from the welding member and thereby bring about a drastic lowering in the fuel permeability of the modified polyethylene, so that it is possible to lower the proportion of the mineral to a still further extent and ensure the still higher fluidity or moldability of the molten resin which is used to make the tank joint part.
According to a third aspect of this invention, the mineral occupies a proportion of 2 to 10% by weight in the modified polyethylene of the first and second aspects. The mineral proportion as stated is preferred for achieving a particularly good result in lowering the fuel permeability of the modified polyethylene, while ensuring the satisfactory fluidity or moldability of the molten resin when molding the tank joint part. If the mineral proportion is lower than 2% by weight, it may be impossible to lower the fuel permeability of the modified polyethylene satisfactorily. If it exceeds 10% by weight, satisfactory fluidity or moldability of the molten modified polyethylene may not be attained in molding the tank joint part. A still more preferable mineral proportion is from 2 to 5% by weight.
According to a fourth aspect of this invention, the modified polyethylene of the first to third aspects is of the carboxylic acid-modified, carboxylic anhydride-modified, or base-modified type. Any such type of polyethylene is excellent especially in weldability to the outer surface of the fuel tank and the main body of the tank joint part and in dispersibility of the mineral.
According to a fifth aspect of this invention, the resin of the main body of the first to fourth aspects is an alloy of a resin of low fuel permeability and a polyolefin elastomer, or the tank joint part includes an intermediate member formed of such an alloy and interposed between its main body and welding member. The alloy is such a material that when swelling with fuel, its swelling may not differ by any more than 10% from that of HDPE forming the outer surface of the fuel tank or that of modified polyethylene, while it shows a high welding strength of, say, at least 2 MPa when it is welded to either, so that hardly any cracking or fracture may occur at the welded portion of the main body.
According to a sixth aspect of this invention, the resin in the alloy of the fifth aspect is preferably a polyphenylene sulfide (PPS), polyester, polyacetal (POM) or polyamide (PA) resin, or an ethylene-vinyl alcohol copolymer (EVOH).
According to a seventh aspect of this invention, the resin of the main body of the first to sixth aspects, or of the main body and the intermediate member contains layers of a nano-layered mineral dispersed therein, so that the fuel permeability of the main body (and the intermediate member) can be still more lowered.
According to an eighth aspect of this invention, the welding member and the main body are a product of two-color molding, or the welding member, intermediate member and main body are a product of multi-color molding. Two-color molding is a method in which two kinds of molten resins are injected from separate injection nozzles into a mold successively or simultaneously to make a resinous product composed of two portions or members. Multi-color molding is a method in which three or more kinds of molten resins are likewise injected into a mold to make a resinous product composed of three or more portions or members. As a product of two-color or multi-color molding generally has a high bonding strength at the bonded portions, the joint part according to this invention has an improved bonding strength between the welding member and main body, between the welding and the intermediate members, and between the intermediate member and main body. A broader range of materials can, therefore, be employed to make a product which is satisfactory in bonding strength.
According to a ninth aspect of this invention, there is provided a process for manufacturing an annular molded resin product, wherein the process comprises injecting a molten resin containing a nano-layered mineral dispersed therein in layers into an annular mold cavity through a film gate formed at its top along its whole circumference. The process makes it possible to manufacture easily and effectively an annular molded resin product containing mineral layers oriented substantially at right angles to its radius. The process or its advantages will be described in detail based on FIG. 1. FIG. 1 shows at (a) an annular molded resin product 1 made by the injection molding of a molten resin containing a nano-layered mineral through a film gate 2 formed at the top of an annular mold cavity along its whole circumference. The molten resin flows down along the whole circumference of the annular mold cavity and the molded product 1, therefore, contains the mineral 3 oriented substantially at right angles to its radius, as shown in FIG. 1 at (b) or (c) On the other hand, FIG. 2 shows at (a) an annular molded product 1 made by the injection molding of a molten resin containing a nano-layered mineral through a one-point gate 4 formed at the top of an annular mold cavity. The molten resin flows horizontally along the annular mold cavity and the mineral 3 in the molded product is oriented as shown in FIG. 2 at (b) or (c) and fails to be oriented substantially at right angles to its radius.
According to a tenth aspect of this invention, there is provided a process for manufacturing an annular molded resin product, which comprises the steps of extruding a molten resin containing a nano-layered mineral dispersed in layers into a cylindrical molded product; and cutting an annular molded product having a required thickness from the cylindrical molded product. The process likewise makes it possible to manufacture easily and effectively an annular molded product containing mineral layers oriented substantially at right angles to its radius. The cylindrical molded product contains the mineral layers oriented along its wall in the direction of its extrusion, and the annular resin product made by cutting it, therefore, contains the mineral layers oriented substantially at right angles to its radius.
The above and other features and advantages of this invention will become apparent from the following description and the accompanying drawings.